Postheparin Plasma Lipoprotein Lipase Research Articles

A sandwich-enzyme immunoassay for the quantification of lipoprotein lipase and hepatic triglyceride lipase in human postheparin plasma using monoclonal antibodies to the corresponding enzymes

We have developed a sandwich-enzyme immunoassay (EIA) for the quantification of lipoprotein lipase (LPL) and hepatic triglyceride lipase (HTGL) in human postheparin plasma (PHP) using monoclonal antibodies (MAbs) directed against the corresponding enzymes purified from human PHP. The sandwich-EIA for LPL was performed by using the combination of two distinct types of anti-LPL MAbs that recognize different epitopes on the LPL molecule. The immunoreactive mass of LPL was specifically measured using a beta-galactosidase-labeled anti-LPL MAb as an enzyme-linked MAb, an anti-LPL MAb linked with the bacterial cell wall as an insolubilized MAb, and purified human PHP-LPL as a standard. The sandwich-EIA for HTGL was carried out by using two distinct anti-HTGL MAbs that recognize different epitopes on HTGL. The limit of detection was 20 ng/ml for LPL and 60 ng/ml for HTGL. Each method yielded a coefficient of variation of less than 6% in intra- and inter-assays, and a high concentration of triglyceride did not interfere with the assays. The average recovery of purified human PHP-LPL and -HTGL added to human PHP samples was 98.8% and 97.5%, respectively. The immunoreactive masses of LPL and HTGL in PHP samples, obtained at a heparin dose of 30 IU/kg, from 34 normolipidemic and 20 hypertriglyceridemic subjects were quantified by the sandwich-EIA. To assess the reliability of the measured mass values, they were compared with the corresponding enzyme activities measured by selective immunoinactivation assay using rabbit anti-human PHP-LPL and -HTGL polyclonal antisera. Both assay methods yielded a highly significant correlation in either normolipidemic (r = 0.945 for LPL; r = 0.932 for HTGL) or hypertriglyceridemic subjects (r = 0.989 for LPL; r = 0.954 for HTGL). The normal mean (+/- SD) level of lipoprotein lipase mass and activity in postheparin plasma was 223 +/- 66 ng/ml and 10.1 +/- 2.9 mumol/h per ml, and that of hepatic triglyceride lipase mass and activity was 1456 +/- 469 ng/ml and 26.4 +/- 8.7 mumol/h per ml, respectively. The present sandwich-enzyme immunoassay methods make it possible to study the molecular nature of LPL and HTGL in PHP from patients with either primary or secondary hyperlipoproteinemia.

Effect of Insulin Therapy on Metabolic Fate of Apolipoprotein B–Containing Lipoproteins in NIDDM

Non-insulin-dependent diabetic (NIDDM) subjects exhibit abnormalities in their plasma lipid and lipoprotein profiles that increase the risk of ischemic heart disease. This study was designed to examine the metabolic behavior of very-low-density (VLDL), intermediate-density (IDL), and low-density (LDL) lipoproteins in NIDDM patients before treatment and after 4 wk of insulin therapy. Basal turnover studies of 131I-labeled VLDL1 (svedberg units [Sf] 60-400) and 131I-labeled VLDL2 (Sf 20-60) apolipoprotein B (apoB) were conducted in a group of seven NIDDM patients who had been off oral therapy for 1 wk. The subjects exhibited higher than normal transport rates for VLDL1 and a diminished input of apoB into the VLDL2 density range. These observations are concordant with the hypothesis that NIDDM patients overproduce VLDL triglyceride but not apoB. VLDL1 and VLDL2 were converted to IDL and ultimately to LDL at approximately normal rates, although the delipidation pathway by which apoB-containing particles were processed exhibited different properties from that seen in control subjects. Insulin therapy reduced plasma triglyceride by 38%, and this was associated with a 41% fall in VLDL1 mass (P less than 0.01). VLDL2 was less affected (19% reduction, P less than 0.05), IDL was unchanged, and LDL fell 17% (P less than 0.05). Repeat metabolic studies revealed that the major effects of insulin were to reduce VLDL1-apoB transport (from 811 to 488 mg/day) and increase the direct input of VLDL2 into the plasma (from 182 to 533 mg/day, P less than 0.05). These alterations in VLDL production led to normalization of apoB kinetics in IDL and LDL. The fractional catabolic rate of LDL increased 19% (P less than 0.05), whereas direct input into this fraction, which had been high before treatment, was reduced. Postheparin plasma lipoprotein lipase (LPL) and hepatic lipase levels were unaffected by insulin, although the hormone did increase LPL in adipose tissue. This lack of effect on lipase activities correlated well with the observation that the rates of catabolism of apoB in VLDL1, VLDL2, and IDL were not significantly affected by insulin therapy.

Amiodarone-Induced Changes in Lipid Metabolism

Hypothyroidism is a major cause of secondary hypercholesterolemia. Amiodarone treatment alters both the levels of serum lipids and thyroid hormones. We investigated whether the amiodarone-induced changes in lipid metabolism are related to the changes in thyroid hormone levels. Eighteen patients received amiodarone (31 +/- 3 g cumulative dose) for six weeks. Serum triglyceride, total-cholesterol, high density lipoprotein-cholesterol and its subfractions, apolipoproteins B and AI, and plasma post-heparin lipoprotein lipase and hepatic triglyceride lipase activities were determined. Amiodarone treatment caused significant increases in serum total-cholesterol (baseline 4.4 +/- 0.21 (SE), 6 weeks 5.12 +/- 0.26 mmol/l, P less than 0.01), in low density lipoprotein cholesterol (baseline 2.61 +/- 0.26, 6 weeks 3.36 +/- 0.21 mmol/l, P less than 0.05) and in apolipoprotein B (baseline 1.95 +/- 0.15, 6 weeks 2.26 +/- 0.13 mmol/l, P less than 0.01) concentrations. Serum high density lipoprotein and its subfractions, or apolipoprotein AI levels did not change. Plasma post-heparin lipoprotein lipase activity increased (baseline 137 +/- 21, 6 weeks 168 +/- 21 U/ml, P less than 0.01) while hepatic triglyceride lipase did not change. Amiodarone also caused an increase in serum thyroxine (baseline 110 +/- 8, 6 weeks 136 +/- 6 mmol/l, P less than 0.05), although values remained in euthyroid range. In summary, amiodarone therapy increased the concentrations of atherogenic lipoproteins in the serum similar to that seen in hypothyroidism. On the other hand the effect of amiodarone on lipoprotein lipase was opposite to that seen in hypothyroidism. Therefore, amiodarone-induced changes in lipid metabolism cannot be explained solely on the basis of the changes in circulating thyroid hormone levels.

Correlates of plasma very-low-density lipoprotein concentration and composition in premenopausal women

Potential correlates of plasma very-low-density lipoprotein (VLDL) concentration and composition were studied in a sample of 75 premenopausal women. Fasting plasma free fatty acid (FFA) levels, as well as plasma glucose and insulin levels in the fasting state and during an oral glucose tolerance test, displayed significant positive correlations with plasma triglyceride (TG) and VLDL-TG levels ( P < .005). Plasma post-heparin lipoprotein lipase (LPL) activity, measured in a subsample of 31 women from the original sample, was negatively correlated with plasma TG, VLDL-cholesterol (CHOL), VLDL-TG, and VLDL-apolipoprotein (apo) B concentrations (.005 > P < .05). Multivariate analyses showed that, after LPL was considered, the insulin area was the only other metabolic variable studied that was significantly correlated with VLDL-apo B concentration, whereas fasting FFA levels were significantly correlated with plasma TG and VLDL-TG levels. ANOVA revealed that plasma VLDL-CHOL, VLDL-TG, and VLDL-apo B levels were not associated with the glucose area, but were significantly associated with the insulin area ( P < .005). When the effect of insulin area was controlled for, the plasma FFA levels did not contribute significantly to the variance in VLDL-CHOL and VLDL-apo B, but showed an independent effect on VLDL-TG levels ( P < .05). Finally, stepwise multiple regression analyses indicated that once the variance explained by plasma LPL activity and by the insulin area was considered, no other metabolic variable could account for the variation in VLDL-CHOL and VLDL-apo B levels, whereas fasting FFA levels explained a further 5% of the VLDL-TG variance and one third of the variance observed in the VLDL-TG/apo B ratio. These results suggest that high plasma insulin levels and a low post-heparin plasma LPL activity are conditions associated with an increased concentration of VLDL, whereas high FFA levels are rather associated with an enrichment of VLDL with triglycerides.

Relationship between Post-Heparin Plasma Lipases, Triglycerides and High Density Lipoproteins in Normal Subjects

The relationship between plasma lipids and lipoproteins and the lipolytic activities of post-heparin plasma lipoprotein lipase (LpL) and hepatic-triglyceride lipase (H-TGL) was examined in normal subjects. Seven males and six females were given a high fat diet [15% carbohydrate (CARB), 65% fat, 20% protein] for 2 weeks followed by 4 weeks of a high CARB diet (65% CARB, 15% fat, 20% protein). Changes in plasma triglyceride concentrations associated with diet were negatively correlated with changes in HDL-C (r = -0.533, P less than 0.001) and the HDL subfraction HDL2b (r = -0.308, P less than 0.001). The activity of LpL in post-heparin plasma was positively correlated with changes in plasma HDL-C (r = 0.668, P less than 0.001) and HDL2b (r = 0.457, P less than 0.001), and negatively with plasma triglycerides (r = -0.546, P less than 0.001). Changes in H-TGL activity were negatively correlated with changes in HDL2b (r = -231, P less than 0.05) and positively correlated with HDL-C (r = 0.326, P less than 0.01). These results in normal subjects provide further evidence that LpL and H-TGL are important enzymes in the metabolism of plasma lipoproteins and that changes in their activities contribute to plasma lipid and lipoprotein concentrations.

Postprandial lipemia and lipoprotein lipase in the rabbit are modified by olive and coconut oil.

Feeding a 14% coconut oil/0.5% cholesterol (CNO/chol) diet to rabbits resulted in plasma triglycerides that were, on average, 15 times higher than basal levels. Plasma triglycerides in rabbits fed a 14% olive oil/0.5% cholesterol (OO/chol) diet were significantly below baseline levels. Differences in postprandial triglyceride response and postheparin plasma lipoprotein lipase activity (LPL) in various feeding conditions were studied to determine the mechanism of the hypertriglyceridemia. Postprandial triglyceride responses after the first high fat/cholesterol meal were more prolonged in CNO/chol rabbits than in OO/chol rabbits; postprandial triglyceride responses after chronic CNO/chol feeding were significantly greater compared to OO/chol rabbits. When long-term CNO/chol rabbits were given one OO/chol or corn oil/chol meal, postprandial triglyceride peaks were greatly diminished, suggesting that these unsaturated fat meals may alter triglyceride clearance capacity. LPL activity was 400% higher than basal levels in chronically fed OO/chol rabbits but changed very little in chronically fed CNO/chol rabbits. Twenty-four hours after a single OO/chol meal was fed to chow-fed rabbits, LPL doubled; one CNO/chol meal was associated with only a 40% increase. Feeding a single OO/chol or corn oil/chol meal to chronically fed CNO/chol rabbits resulted in a 30% to 50% increase in LPL by 24 hours. Thus, the hypertriglyceridemia in CNO/chol rabbits may result in part from a decreased clearance capacity due to a lack of increase in LPL activity, while increased LPL may be partially responsible for the hypotriglyceridemia observed in OO/chol feeding. Aortic cholesterol was substantially higher in CNO/chol rabbits. Triglyceride was approximately eight times greater in livers from CNO/chol-fed rabbits than in those fed OO/chol, but liver cholesterol was only about one-third as much as that in OO/chol rabbits.

Lipoprotein lipaseBethesda: a single amino acid substitution (Ala-176----Thr) leads to abnormal heparin binding and loss of enzymic activity.

The molecular defect that leads to a deficiency of lipoprotein lipase (LPL) activity in the proband from a Bethesda kindred has been identified. The pre- and post-heparin plasma LPL mass in the proband was elevated when compared to controls; however, there was no detectable LPL activity, indicating the presence of a defective enzyme (termed LPLBethesda). Analysis of the patient's post-heparin plasma by heparin-Sepharose affinity chromatography demonstrated that the mutant LPL had an altered affinity for heparin. Southern blot hybridization of the gene for LPLBethesda revealed no major rearrangements. Northern blot analysis of LPLBethesda mRNA from patient monocyte-derived macrophages revealed normal-sized mRNAs (3.4 and 3.7 kilobases) as well as normal cellular mRNA levels when compared to control macrophages. Sequence analysis of polymerase chain reaction-amplified LPL cDNA revealed a G----A substitution at position 781 of the normal LPL gene that resulted in the substitution of an alanine for a threonine at residue 176 and the loss of an SfaNI site present in the normal LPL gene. Amplification of cDNA by the PCR followed by digestion with SfaNI established that the patient was a true homozygote for the mutation. Expression of LPL cDNA in COS-7 cells resulted in the synthesis of a nonfunctional LPL enzyme establishing that the Ala----Thr substitution was the mutation responsible for the inactive LPL. The identification of this mutation in the LPL gene defines a region of the LPL enzyme, at Ala-176, that is essential for normal heparin-binding and catalytic activity. We propose that an amino acid substitution in this critical region of LPLBethesda results in the synthesis of a nonfunctional enzyme that leads to the chylomicronemia syndrome expressed in this proband.

Effects of omega-3 fish oils on plasma lipids, lipoprotein composition, and postheparin lipoprotein lipase in women with IDDM

Effects of omega-3 fish oils on plasma lipids, lipoprotein composition, and postheparin lipoprotein lipase in women with IDDM

Excess parathyroid hormone adversely affects lipid metabolism in chronic renal failure

Hyperlipidemia is common in chronic renal failure (CRF), but the underlying mechanisms are not clearly defined. Certain data points toward a potential role for the state of secondary hyperparathyroidism of CRF in its pathogenesis. We examined the effects of parathyroid hormone (PTH) on lipid metabolism utilizing intravenous fat tolerance test (IVFTT) and post-heparin lipolytic activity in five normal dogs, in six animals with CRF and secondary hyperparathyroidism (NPX) and in six normocalcemic-thyroparathyroidectomized dogs (NPX-PTX) with comparable degree and duration of CRF. NPX dogs had fasting hypertriglyceridemia (82 + 6.0 mg/dl vs. 49 +/- 2.7 mg/dl in normal dogs, P less than 0.01), abnormal IVFTT, and reduced post-heparin plasma LPL activity (151 +/- 10 vs. 275 +/- 15 mumol fatty acids/ml/min in normal dogs, P less than 0.01). The NPX-PTX dogs had normal fasting levels of serum triglycerides (42 +/- 0.6 mg/dl), normal IVFTT, and normal post-heparin plasma LPL (317 +/- 19 mumol fatty acids/ml/min) despite CRF. Post-heparin HL activity in plasma was not different between NPX and NPX-TPX dogs. The results show that excess blood levels of PTH and not other consequences of CRF are mainly responsible for the abnormalities in lipid metabolism. The data are consistent with the notion that excess PTH reduces post-heparin LPL activity in plasma, which in turn results in impaired lipid removal from the circulation and consequently hyperlipidemia.

Postheparin plasma lipoprotein and hepatic lipase are determinants of hypo- and hyperalphalipoproteinemia.

To study the role of the two postheparin plasma lipolytic enzymes, lipoprotein lipase (LPL) and hepatic lipase (HL) in high density lipoprotein (HDL) metabolism at a population level, we determined serum lipoproteins, apoproteins A-I, A-II, B, and E, and postheparin plasma LPL and HL activities in 65 subjects with a mean HDL-cholesterol of 34 mg/dl and in 62 subjects with a mean HDL-cholesterol of 87 mg/dl. These two groups represented the highest and lowest 1.4 percentile of a random sample consisting 4,970 subjects. The variation in HDL level was due to a 4.1-fold difference in the HDL2 cholesterol (P less than 0.001) whereas the HDL3 cholesterol level was increased only by 32% (P less than 0.001) in the group with high HDL-cholesterol. Serum apoA-levels were 128 +/- 2.2 mg/dl and 210 +/- 2.8 mg/dl (mean +/- SEM) in hypo- and hyper-HDL cholesterolemia, respectively. Serum apoA-II concentration was elevated by 28% (P less than 0.001) in hyperalphalipoproteinemia. The apoA-I/A-II ratio was elevated only in women with high HDL-cholesterol but not in men, suggesting that elevation of apoA-I is involved in hyperalphalipoproteinemia in females, whereas both apoA proteins are elevated in men with high HDL cholesterol. Serum concentration of apoE and its phenotype distribution were similar in the two groups. The HL activity was reduced in the high HDL-cholesterol group (21.2 +/- 1.5 vs. 38.5 +/- 1.8 mumol/h/ml, P less than 0.001), whereas the LPL activity was elevated in the group with high HDL-cholesterol compared to subjects with low HDL-cholesterol (27.8 +/- 1.3 vs. 19.9 +/- 0.8 mumol/h/ml, P less than 0.001). The HL and LPL activities correlated in opposing ways with the HDL2 cholesterol (r = 0.57, P less than 0.001 and r = 0.51, P less than 0.001, respectively), and this appeared to be independent of the relative ponderosity by multiple correlation analysis. The results demonstrate major influence of both HL and LPL on serum HDL cholesterol concentration at a population level.

Role of hepatic-triglyceride lipase activity in the association between intra-abdominal fat and plasma HDL cholesterol in obese women.

Intra-abdominal fat content is an important variable in the association between regional body fat distribution and plasma high density lipoprotein (HDL) cholesterol levels. In the present study, we report on the role of plasma postheparin lipases as well as abdominal and femoral adipose tissue lipoprotein lipase activities in the association between body fat distribution and plasma lipoprotein levels. Postheparin plasma lipoprotein lipase (LPL), hepatic-triglyceride lipase (H-TGL), abdominal and femoral adipose tissue (AT)-LPL activities and plasma lipoprotein levels were measured after an overnight fast in a sample of 16 obese women (ages 36.0 +/- 6.1 years [mean +/- SD], percent body fat 46% +/- 6%). Computed axial tomography was used to assess body fat distribution. Plasma postheparin LPL activity was neither correlated with total adiposity nor with the level of intra-abdominal fat. Intra-abdominal fat deposition was, however, positively correlated with H-TGL activity (r = 0.66, p less than 0.005). Furthermore, covariance analysis showed that the association between intra-abdominal fat and H-TGL was independent from total adiposity. Plasma postheparin LPL and abdominal AT-LPL activities showed no significant correlation with plasma lipoprotein levels, whereas femoral AT-LPL activity was positively correlated with the HDL2 cholesterol/HDL3 cholesterol ratio (r = 0.51, p less than 0.05). H-TGL activity was, however, negatively correlated with HDL2 cholesterol (r = -0.60, p less than 0.05), but not with HDL3 cholesterol (r = -0.28, NS). These results suggest that the high H-TGL activity in obese women with excess deep abdominal fat could be responsible for the reduction in plasma HDL2 cholesterol levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of cholesterol feeding on lipolytic activities in high- and low-responding rhesus monkeys.

We compared the activities of lipoprotein (LPL) and hepatic lipase (HL) in postheparin plasma in groups of high- and low-responding rhesus monkeys fed a low cholesterol diet followed by a high cholesterol diet. Cholesterol feeding resulted in a two-phase response in lipolytic activities: an initial phase lasting about 21 days that was similar in the two groups, followed by the second phase in which major differences became apparent between the groups. In the initial phase, LPL and HL activities increased along with plasma cholesterol and high density lipoprotein (HDL) cholesterol, but there was no change in plasma triglycerides or apolipoprotein (apo) A-I levels. These changes suggest that both high and low responders respond in a similar manner to metabolize an increased lipid load and that both groups continue to remove triglyceride efficiently while cholesterol accumulation begins. The second phase (between 21 and 42 days and thereafter) in high responders was characterized by a decrease in LPL and HL activities along with plasma HDL cholesterol and apo A-I levels, continued increase in plasma cholesterol, and a slow increase in plasma triglycerides. In low responders, LPL activity was maintained at a high level, HL activity decreased to the basal level, and plasma lipids were unchanged. All changes occurred simultaneously, suggesting metabolic relationships between plasma lipolytic activities, plasma lipids, and apolipoprotein.

Detection and characterization of the heterozygote state for lipoprotein lipase deficiency.

Because there are no characteristic clinical or biochemical manifestations, the heterozygote state for lipoprotein lipase (LPL) deficiency has been difficult to detect. Measurements of postheparin plasma LPL activity and of LPL mass were performed in six families of probands with LPL deficiency to characterize the heterozygote state. LPL mass was measured in a sandwich enzyme-linked immunosorbent assay (ELISA) using a monoclonal antibody (5D2) that had been produced against bovine milk LPL. Thirteen obligate heterozygotes from these families had reduced LPL activity and mass below the 95th percent confidence limits of 34 normal controls, while one obligate heterozygote had LPL activity and mass between the 90th and 95th percent confidence limits. Potential heterozygotes in these families were identified as normal (n = 8) or heterozygotes (n = 6) by comparison to the 95th percent confidence limits of the controls. Some relatives in four of the six families exhibited mild hyperlipidemia, similar to the pattern seen in familial combined hyperlipidemia (FCHL). The hyperlipidemia segregated with the heterozygote state for LPL deficiency in these families (p less than 0.03). High density lipoprotein (HDL) cholesterol was significantly reduced in the heterozygotes for LPL deficiency (p less than 0.01). The measurement of LPL activity and mass allows identification of the heterozygote state for LPL deficiency, which is characterized by variable expressions of hyperlipidemia and reduced HDL cholesterol. These results suggest that the heterozygote state for LPL deficiency may form one subset of FCHL.

Impaired triacylglycerol catabolism in hypertriglyceridemia of the diabetic, cholesterol-fed rabbit: a possible mechanism for protection from atherosclerosis

The etiology of the hypertriglyceridemia in alloxan-diabetic rabbits was studied by two independent methods. Production and removal rates of VLDL triacylglycerol were measured in diabetic rabbits by injection of [3H]palmitate-labelled VLDL. Similarly, triacylglycerol total removal rates were determined in non-diabetic rabbits which were infused with Intralipid to mimic the plasma triacylglycerol concentrations of diabetic rabbits. Compared to nondiabetic rabbits, triacylglycerol removal rats were decreased in diabetic rabbits, particularly at higher levels of plasma triacylglycerol. During cholesterol and triacylglycerol supplementation of the diet, post-heparin plasma lipoprotein lipase activity of diabetic rabbits with severe hypertriglyceridemia averaged 36% of that of nondiabetics, suggesting an impaired triacylglycerol removal capacity. Furthermore, plasma triacylglycerol was inversely related to post-heparin plasma lipoprotein lipase activity among diabetic rabbits. VLDL triacylglycerol production increased with increasing plasma triacylglycerol concentration among diabetic cholesterol-fed rabbits with moderately severe hypertriglyceridemia, but reached an apparent plateau among rabbits with plasma triacylglycerol concentrations from approx. 2000-9000 mg/dl. Thus, severe hypertriglyceridemia in this model of insulin deficiency can be attributed only partially to VLDL hypersecretion, whereas a removal defect, resulting in saturation of the triacylglycerol removal mechanism, appears to be largely responsible. The impaired removal of plasma triacylglycerol is also related to the presence of cholesterol predominantly in lipoproteins of increased size. The data support the hypothesis that protection against atherosclerosis in cholesterol-fed diabetic rabbits results from exclusion of very large cholesterol-containing lipoproteins from the arterial wall.

Effect of marginal zinc deficiency on lipoprotein lipase activities in postheparin plasma, skeletal muscle and adipose tissues in the rat.

The activities of lipoprotein lipase in postheparin plasma, retroperitoneal adipose and gastrocnemius muscle tissues were determined in the rats fed 2.8 ppm of dietary zinc for eight weeks, as compared with pair-fed and ad libitum-fed rats given 30.8 ppm of zinc. The postheparin lipoprotein lipase activity, as determined by using a lipid emulsion labeled with [3H]triolein as the substrate, was significantly lower in the first group of rats, relative to that in the second and third groups. Tissue lipoprotein lipase activities were compared using the lipid emulsion and activator serum obtained from the zinc-deficient rats and the ad libitum-fed rats. The activator sera were devoid of very low density and low density lipoproteins, but enriched in high density lipoproteins. Muscle lipoprotein lipase activities were significantly lower when assayed with the activator serum from the zinc-deficient compared with the activities determined with the activator serum from the ad libitum-fed. Similarly, muscle lipoprotein lipase activities were lower in all groups when [3H]-triolein-labeled chylomicrons from the zinc-deficient were used as the substrate, compared with the activities determined using the chylomicrons from the ad libitum-fed. Lipoprotein lipase activities in the adipose tissues were not affected by the different sources of the activator sera and chylomicrons. The results strongly suggest that the decrease in postheparin lipoprotein lipase activity in zinc deficiency is not due to changes in tissue lipoprotein lipase enzyme per se, but to compositional alterations in chylomicrons and high density lipoprotein, particularly, with regard to C apolipoproteins, modulators of lipoprotein lipase activity.

Nicotine does not affect plasma lipoprotein concentrations in healthy men

The effects of nicotine administration (2 mg eight-times daily as nicotine chewing gum for two weeks) on plasma lipid and lipoprotein concentrations were studied in young healthy volunteers. Plasma levels of the nicotine metabolite, cotinine, reached levels comparable to those seen in smokers. Plasma concentrations of triglyceride, cholesterol, HDL cholesterol, LDL cholesterol, and apolipoproteins AI and B, were determined repeatedly before, during and after cessation of nicotine intake. All these variables, as well as the activities of lipoprotein lipase and hepatic lipase in post-heparin plasma, remained unchanged throughout the study. The results strongly suggest that the effects of smoking on plasma lipoprotein metabolism are not mediated via nicotine, and indicate that nicotine chewing gum, when used therapeutically in anti-smoking programmes, does not carry the same metabolic side effects as smoking.

Modest Changes in High-Density Lipoprotein Concentration and Metabolism With Prolonged Exercise Training

High-density lipoprotein (HDL) metabolism was studied in eight sedentary men before and after 14 and 32-48 weeks of exercise training. Subjects rode stationary bicycles 1 hour daily, 5 days each week for 14 weeks (n = 8), and 4 days each week thereafter for a total of 32-48 weeks (n = 7) of training. HDL metabolism was assessed with 125I-radiolabeled autologous HDL while subjects consumed defined diets. Maximal oxygen uptake increased 26 +/- 7% (p less than 0.001) after 14 weeks but did not increase further with more prolonged training. Body weight and estimated body fat did not change. HDL cholesterol increased 5 +/- 3 mg/dl, and triglycerides decreased 19 +/- 23 mg/dl after 14 weeks (p less than 0.025 for both), but there were no additional changes with continued training. Postheparin plasma lipoprotein lipase activity was 22% higher than baseline activity after both 14 (p less than 0.025) and 32 or more weeks of exercise. In contrast, hepatic triglyceride lipase activity was 16 +/- 8% and 15 +/- 8% lower than baseline at each measurement (p less than 0.005 for both). The disappearance rate of triglycerides after an intravenously administered fat solution was 24 +/- 24% higher at 14 weeks and 49 +/- 18% (p less than 0.005) higher after more prolonged training. Total and low-density lipoprotein cholesterol and apolipoprotein A-I and A-II concentrations at the end of study were not different from initial values. Plasma volume was 8% above initial values at both post-training measurements. The biological half-life of apolipoprotein A-I was unchanged at 14 weeks but was 10 +/- 13% longer (p = 0.07) and increased in all but one subject at the end of the study. Half-life for apolipoprotein A-II was 8 +/- 8% (p = 0.031) and 11 +/- 14% (p = 0.06) above baseline at 14 and 32 or more weeks, respectively. The synthetic rates for apolipoproteins A-I and A-II were not different from baseline values at 32-48 weeks. We conclude that 8-11 months of exercise training in previously sedentary men enhances fat tolerance and increases HDL cholesterol concentrations by prolonging HDL survival. The changes in HDL apolipoprotein survival, however, do not approximate the differences previously noted between elite endurance athletes and sedentary men. Changes in HDL cholesterol concentration were not large and suggest that the potential for exercise-related changes in HDL may be modest in many subjects.

Effect of copper deficiency on the lymphatic absorption of cholesterol, plasma chylomicron clearance, and postheparin lipase activities.

The lymphatic absorption of cholesterol and plasma clearance of chylomicrons were investigated in Cu-deficient rats (CuD) fed 0.5 mg Cu/kg diet, as compared with Cu-adequate control rats (CuA) fed 7.5 mg/kg diet. Cholesterol absorption was measured by the 14C-radioactivity appearing in the mesenteric lymph at hourly intervals for 8 hr after an intraduodenal dose of [14C]cholesterol. The plasma clearance of chylomicrons was measured at 3, 6, and 10 min after an intravenous dose of chylomicrons labeled in vivo with [3H]retinyl ester. Cumulative [14C]cholesterol absorption and total lymphatic output of cholesterol were significantly decreased in CuD at 4 hr and thereafter, with no change in percentage distribution of free and esterified cholesterol. Over an 8-hr period, 7.3% of the dose was absorbed by CuD and 9.2% by CuA. When [3H]chylomicrons, obtained from a CuD or CuA donor rat, were injected into CuD and CuA recipient rats, the label was cleared faster in CuD during the first 3 min. At 6 and 10 min, however, no significant difference in percentage clearance of the dose was observed between the groups. The half-life (t1/2) of [3H]chylomicrons and the total 3H-radioactivity taken up by the liver during the entire 10-min period did not differ between the groups, regardless of the source of chylomicrons. The activities of both endothelial lipoprotein lipase (LPL) and hepatic lipase (HL) in postheparin plasma were markedly lower in CuD. As expressed in micromoles fatty acid released/hr/ml plasma, the activities of LPL in CuD and CuA were 32.6 +/- 1.9 and 45.6 +/- 1.3, respectively. A similar magnitude of difference was also observed in HL activity. The data provide evidence that copper deficiency impairs the intestinal transport of cholesterol and the peripheral lipolysis of chylomicrons. The data, however, strongly suggest that the hepatic uptake of chylomicron remnants via the apo-E-dependent mechanism may not be impaired in Cu deficiency.

Relationship between lipoprotein lipase activity and plasma sex steroid level in obese women.

In obese women (n = 16) at their weight, fasting adipose tissue lipoprotein lipase (LPL) activity, obtained by elution with serum and heparin at 4 degrees and 37 degrees C, was inversely correlated to plasma estradiol levels (r = -0.724; P = 0.002) and (r = -0.641; P = 0.010), respectively. Furthermore, fasting postheparin plasma LPL activity during a heparin infusion, showed an even stronger inverse correlation to plasma estradiol when measured at 60 min (r = -0.815; P less than 0.001). None of the above parameters was correlated to the body mass index. Postprandial LPL activity in postheparin plasma, measured 10 min after a heparin injection, showed a strong positive correlation with plasma free testosterone (r = 0.780; P = 0.001). Neither of these parameters was correlated with the body mass index. The origin of this LPL activity is presently unknown but could conceivably represent a pool of LPL from skeletal muscle. Since it has been shown convincingly that estrogen decreases adipose tissue LPL activity in the rat, the present studies strongly suggest that estradiol is a major negative regulator of fasting adipose tissue LPL activity in women.

Modest changes in high-density lipoprotein concentration and metabolism with prolonged exercise training.

High-density lipoprotein (HDL) metabolism was studied in eight sedentary men before and after 14 and 32-48 weeks of exercise training. Subjects rode stationary bicycles 1 hour daily, 5 days each week for 14 weeks (n = 8), and 4 days each week thereafter for a total of 32-48 weeks (n = 7) of training. HDL metabolism was assessed with 125I-radiolabeled autologous HDL while subjects consumed defined diets. Maximal oxygen uptake increased 26 +/- 7% (p less than 0.001) after 14 weeks but did not increase further with more prolonged training. Body weight and estimated body fat did not change. HDL cholesterol increased 5 +/- 3 mg/dl, and triglycerides decreased 19 +/- 23 mg/dl after 14 weeks (p less than 0.025 for both), but there were no additional changes with continued training. Postheparin plasma lipoprotein lipase activity was 22% higher than baseline activity after both 14 (p less than 0.025) and 32 or more weeks of exercise. In contrast, hepatic triglyceride lipase activity was 16 +/- 8% and 15 +/- 8% lower than baseline at each measurement (p less than 0.005 for both). The disappearance rate of triglycerides after an intravenously administered fat solution was 24 +/- 24% higher at 14 weeks and 49 +/- 18% (p less than 0.005) higher after more prolonged training. Total and low-density lipoprotein cholesterol and apolipoprotein A-I and A-II concentrations at the end of study were not different from initial values. Plasma volume was 8% above initial values at both post-training measurements. The biological half-life of apolipoprotein A-I was unchanged at 14 weeks but was 10 +/- 13% longer (p = 0.07) and increased in all but one subject at the end of the study. Half-life for apolipoprotein A-II was 8 +/- 8% (p = 0.031) and 11 +/- 14% (p = 0.06) above baseline at 14 and 32 or more weeks, respectively. The synthetic rates for apolipoproteins A-I and A-II were not different from baseline values at 32-48 weeks. We conclude that 8-11 months of exercise training in previously sedentary men enhances fat tolerance and increases HDL cholesterol concentrations by prolonging HDL survival. The changes in HDL apolipoprotein survival, however, do not approximate the differences previously noted between elite endurance athletes and sedentary men. Changes in HDL cholesterol concentration were not large and suggest that the potential for exercise-related changes in HDL may be modest in many subjects.